1. Field of the Invention
The present invention relates to a direct injection type engine.
2. Description of the Related Art
The output of an internal combustion engine is expressed by the product of the torque and rotational speed. Therefore, there are various combinations of torque and rotational speed giving the same torque. In this case, comparing the case of raising the torque and lowering the rotational speed and the case of lowering the torque and raising the rotational speed in order to obtain the same output, the case of a high torque and low speed is better in fuel economy than a low torque and high speed, but the amount of emission of soot, NOx, and other harmful components increases. A low torque and high speed suffers from worse fuel economy compared with a high torque and low speed, but results in less emission of soot, NOx, and other harmful components.
In a direct injection type internal combustion engine, for example, a compression ignition type internal combustion engine, however, various types of exhaust gas purification catalysts have conventionally been arranged in the engine exhaust passage. These catalysts, however, generally do not activate until 250xc2x0 C. to 300xc2x0 C. or more. As opposed to this, in a compression ignition type internal combustion engine, sometimes the temperature of the exhaust gas falls below 250xc2x0 C. At such times, the catalysts become inactive and therefore the harmful components in the exhaust gas can no longer be purified. Therefore, a compression ignition type internal combustion engine is normally controlled so as to lower the torque and increase the rotational speed so as to keep the amount of emission of harmful components in the exhaust gas low in consideration of times when the temperature of the exhaust gas becomes low.
If the engine is controlled in this way to lower the torque and raise the speed, however, the problem arises of a poor fuel economy.
An object of the present invention is to provide a direct injection type engine capable of suitably treating soot and NOx while maintaining a good fuel economy.
According to a first aspect of the present invention, there is provided a direct injection type engine provided with an exhaust passage, comprising a variable speed transmission connected with the engine and able to freely change a gear ratio; an exhaust purification device arranged in the exhaust passage; and a control device for controlling a torque generated by the engine and a gear ratio of the variable speed transmission; at least two control lines which include a first control line and a second control line at a high torque side and low speed side of the first control line in the same required output being set as engine control lines showing the relationship between the engine rotational speed and required torque required for obtaining a required output, the control device causing the engine to generate a required torque on the first control line in accordance with the required output and controlling the gear ratio of the variable speed transmission to give an engine rotational speed on the first control line in accordance with the required output when the extent of activation of the exhaust purification device is low, the control device causing the engine to generate a required torque on the second control line in accordance with the required output and controlling the gear ratio of the variable speed transmission to give an engine rotational speed on the second control line in accordance with the required output when the extent of activation of the exhaust purification device is high.
According to a second aspect of the present invention, there is provided a direct injection type engine provided with an exhaust passage, comprising a transmission connected with the engine and having a plurality of speeds automatically changeable; an exhaust purification device arranged in the exhaust passage; and a control device for changing a speed of the transmission; first boundary lines and second boundary lines at a lower vehicle speed side than the first boundary lines being set as speed boundary lines indicating the relationship between representative values of the required torque and representative values of the vehicle speed at boundaries of different speeds, the control device changing the speeds at the first boundary lines when the degree of activation of the exhaust gas purification device is low and changing the speeds at the second boundary lines when the degree of activation of the exhaust gas purification device is high.